In forage harvesters, it is useful to sharpen the knives of the chopper arrangement from time to time in order to assure that the knives are sufficiently sharp. In this way, the energy requirement for the chopping are kept low and the quality of the cut is kept high. The chopper arrangement is enclosed by a housing that is provided with openings for the supply and delivery of the harvested crop, but its otherwise closed, in order to prevent a discharge of the harvested crop at undesired locations and a contact of the chopper arrangement with the operator. In order to permit the grinding arrangement to interact with the chopper arrangement, the state of the art provides a access door that can be moved between a chopping position, in which it closes the housing in order to prevent an undesired access to the chopper arrangement, and a grinding position, in which it permits access to an opening in the housing, through which the chopper arrangement can interact with the grinding arrangement. In this position, a visual inspection of the knives and a possible replacement of the knives can also be performed.
The movement of the access door between the aforementioned positions can be performed by an actuator actuated by external forces, particularly an electric linear motor (DE 41 34 957 A) or a rotating electric motor (EP 0 444 916 A) that is connected so as to drive the access door over a drive mechanism. The position of the access door is detected by sensors, particularly limit switches or linear potentiometers, and the actuator is controlled to correspond. Thereby the access door is retained exclusively in the chopping position by the actuator.
In certain operating conditions, particularly if the harvested crop is not delivered properly at the outlet of the chopper arrangement and re-circulates with it or jams the chopper arrangement, relatively intense forces can be applied to the cover arrangement, that can also act in form of impulses or beats, and can be transmitted over the drive mechanism to the actuator and the sensor of the position detection arrangement of the cover arrangement. These forces can lead to damage of the actuator or the sensor.
The problem underlying the invention is seen in the need to overcome the aforementioned problem.